Flashlighting in corners
We regret to hear that you're having this black uniformity problem with your LCD TV!
This is something that is seen in LCD and LED TV and generally, the larger the TV the more likely it will have uniformity issues. The cause is due to improper diffusion of the backlight across the entire screen. Like you, I love Plasma TVs and will be sad to see them go because Plasma TVs have perfect uniformity!(my shameless plug in for plasmas!)
It is possible to fix the flashlighting issue if the problem is due to pressure on the frame of the TV. Tightening or loosening the screws behind the edge of the screen can alleviate the pressure and correct the problem, but I wouldn't advise doing this yourself because even if you could get to those screws, (some TVs do not expose the screws!), a small change of a screw can have a huge impact on the uniformity of the screen!
Edge-lit LED TVs have the worst uniformity issues because the LEDs are on the edge! Full array LEDs have good uniformity because the LEDs are spread out over the screen.
If you are still able to return the TV from where you purchased it, you may want to return it or exchange it, some TVs are more prone to uniformity issues than others and if the TVs were stored incorrectly, even though they do have protection, that might lead to you receiving a defective TV. You did mention that you recently purchased this TV, so if it's within the store return policy, return if and you may want to consider getting a Full Array LED.
Your also expressed concern as to whether or not you would have to always deal with this uniformity issue so it might help you in your decision to know that while this is less likely to happen to a brand new TV, over time, as components age at different rates causing uneven brightness of adjacent LEDs, the issue may appear! It might be worth considering extended warranty that would give you peace of mind!^IFV